The present invention relates to a fail-safe fuel valve employed as a safety device for thermoelectric ignition and more particularly to the mounting of the armature in such a mechanism.
The well known thermoelectric ignition safety devices that serve to shut off the flow of gas to burner equipment in case of extinction of a burner flame or of a pilot, require, as is known, an electromagnet or 2-pole magnetic core, as well as an armature plate mounted at one end of a shaft whose other end carries either a valve or a socket, depending on whether the mechanism is designed to block a flow of gas directly or by the intermediation of levers which may be engaged by the socket. To protect the magnetic core and the armature operating with it, they are surrounded by a non-magnetic metallic protective cover, e.g. of brass, or made of plastic.
In these known devices, the magnetic core is fixed rigidly on a bed-plate. On the other hand, the armature is set on the shaft in such a way that there can exist a certain free motion permitting it to be hinged with respect to the two poles of the magnetic core at the time of the operational motions of the gas equipment in which the electromagnetic safety device is incorporated. Finally, there is used a metallic washer integral with the shaft, or resting against a shoulder of the shaft, whose function, in being applied against the rear face of the armature, is to maintain the armature in a plane generally perpendicular to the shaft, and to serve possibly as a stop against the top of the housing when the armature disengages from the magnetic core.
One disadvantage of this method of mounting of the armature for self-alignment is that wear can occur between the armature and the corresponding part of the shaft to which it is attached. The shaft typically includes a portion of reduced diameter which passes through an aperture in the armature and is then typically riveted over to retain the armature. For example, energizing impulses applied to the electromagnet may cause the armature to rotate relative to the shaft and, as the result, small metallic particles may detach from the armature or from the shaft or from both parts, which particles can become attached to the magnetized surfaces of the electromagnet. These particles can bring about variation in the locking an unlocking characteristics of the valve and may even effect a total alteration of the functioning of the safety device.